Why don't the jaggers use all of their heave weapons in the beginning

Rating: 9/10 (19 July 2013)

I first, i want to say that this movie is really good, and worth to watch. They have done a very good job. The acting, the story, the emotion are good. The only thing i think it missing are the fighting scenes. The jaggers are destroyed so easily, there are only 4 jaggers, and indeed, only 2 can fight.
Most of the fights are just hand-to-hand combat. The 2 jaggers have little time to show their ability. They even cant fire any missile or use any special weapon. They have a lot of heave weapons, but i wonder why they did not use them ( the weapons) in the beginning. Overall, i enjoyed this movie, and some scenes are really moving.